Saw-tooth wave frequency divider circuit

ABSTRACT

In frequency divider circuit for saw-tooth wave including a circuit for producing a saw-tooth wave of a frequency f, a circuit for producing a square wave having a frequency f/2, mixing resistors, and a buffer circuit for obtaining a desired output saw-tooth wave of frequency f/2; the peak amplitude of the square wave is so selected as to be greater than the peak amplitude of the saw-tooth wave of a frequency f before mixing, and the ratio of the resistances of the mixing resistors is so selected that the peak amplitudes of the square wave component and the saw-tooth wave component in the mixed resultant wave become equal after mixing, whereby the resultant saw-tooth wave of a frequency f/2 has an amplitude at least equal to that of the original saw-tooth wave of frequency f.

Tomisawa 51 Mar. 21, 1972 SAW-TOOTH WAVE FREQUENCY DIVIDER CIRCUIT NorioTomisawa, Hamamatsu, Japan inventor:

Assignee: Nippon Gakki Seizo Kabushiki Kaisha,

Hamamatsu-shi, Japan Filed: June 2,1970

Appl.No.: 42,705

Foreign Application Priority Data References Cited UNITED STATES PATENTS2,783,382 2/1957 Bode ..328/39 Primary Examiner-John S. HeymanAttorney-Holman & Stern [5 7] ABSTRACT In frequency divider circuit forsaw-tooth wave including a circuit for producing a saw-tooth wave of afrequency f, a circuit for producing a square wave having a frequencyf/2, mixing resistors, and a buffer circuit for obtaining a desiredoutput saw- June l0. 1969 Japan ..44/45039 tooth wave of frequency flthe p amplitude of the square wave is so selected as to be greater thanthe peak amplitude of U.S.Cl 307/225,307/228, 307/291, the Sawtooth waveof a frequencyfbefore mixing and the 328/158 ratio of the resistances ofthe mixing resistors is so selected Int. Cl ..H03k 21/00, H03k 3/12 thatthe peak amplitudes of the square wave component and Field 0I Search 7/the saw-tooth wave component in the mixed resultant wave 307/29] becomeequal after mixing, whereby the resultant saw-tooth wave of a frequencyf/2 has an amplitude at least equal to that m of the original saw-toothwave of frequency f.

5 Claims, 4 Drawing Figures o- 0 IA 1- '"1 i 4 J: VA 0A i-' -i i l L iI;I|

n 2X I! l I K-Trz l l Ri X O2 P'-1L l R5 RE PATENTEDHARZI I972 FIG. I EAINVENTOR ,2 l 7- MWW AQORNEYS SAW-TOOTH WAVE FREQUENCY DIVIDER CIRCUITBACKGROUND OF THE INVENTION I This invention relates to a sawtooth wavefrequency divider circuit, and more particularly to a type of circuitwherein a sawtooth wave having a frequency f and a square wave having afrequency f/2 are mixed together, and a sawtooth wave of a frequency f/2having the same output level (in crest value) as that of the sawtoothwave of the original frequency f is obtained.

Generally speaking, all of the class A transistor amplifiers, such as anemitter follower circuit and emitter grounded type amplifier circuit,cannot have a 100 percent voltage utility factor 1; (which is the ratioof a distortionless, maximum output voltage Vmax to the power sourcevoltage E). Theoretically, if an ideal transistor is employed, a 100percent of the utility factor 1 ought to be obtained when an emitterresistor only is employed in an emitter follower circuit, or when acollector resistor only is employed in an emitter grounded typeamplifier, both of which are considered to have best voltage utilityfactors.

However, there is no ideal transistor, practically, and because theinput signal cannot be driven to volt due to the existence of arestriction in the cut-off range causedby the base-emitter forwardvoltage drop V (this value is about 0.2 to 0.3 v., in general, forgermanium'transistors and about 0.6 to 0.7 v., for silicon transistors).Furthermore, the output signal cannot be swung to the maximum valuebecause it is limited by a collector-emitter voltage drop V (sat) of thesaturation time (this value ranges approximately from 0.3 to 0.5 v.).

In addition, the coefficient h (current amplification factor) is notlinear, and the amplification factor thereof tends to decrease atportions of the operational characteristic curve near the cut-off rangeand the saturation range. For these reasons, there is no class Aamplifier of capacitor-resistor coupled type having a utility factor[-r]of 100 percent.

On the other hand, since the output of a switching circuit such as aflip-flop has only two states, ON and OFF, the waveform distortion doesnot arise. Furthermore, in the latter case, the input voltage may assumea value which might over-drive the switching circuit. Thus, the onlyfactor which lowers the voltage utility factor 1; in the latter kind ofcircuit is the voltage drop V (sat) only, and therefore a voltageutility factor 1 of almost 100 percent can be easily obtained.

In view of the fact that a great number of the frequency dividercircuits are employed in electronic musical instruments, it is desirablethat the frequency divider circuits be of the type having the largestpossible voltage utility factor 17. If the voltage utility factor ishigher, the required power source voltage can be lowered, and thecomponent elements employed in such circuits may be of lower currentratings, lower breakdown voltages, and lower power ratings. Furthermore,for the purpose of obtaining a good S/N (signal to noise) ratio and forfacilitating the handling thereafter, the signal levels in theelectronic musical instruments should be considerably high. Morespecifically, according to general practice, the signals created in thetone source circuits in an electronic musical instrument must beamplified in their subsequent stage because the signals are attenuatedconsiderably in the keyboard circuits and mixing circuits. Thus, if thesignal levels from the tone source circuits are set higher beforehand,the amplifying stages thereafter required may be reduced and, the SINratios thereof may also be improved.

l-Ieretofore, frequency divider circuits employable for producing asawtooth wave have been known. A typical example of such circuits has anorganization as indicated in FIG. 1 excepting that the peak amplitudesof the original sawtooth wave and the square wave are equal and theresistors R, and R A are made equal rather than different as expected inthe circuit of FIG. 1, and that the DC biasing resistors are notprovided in the mixer circuit.

Now the operation of a prior art circuit will be explained for a betterunderstanding of this invention, referring, for convenience, to FIG. 1,in which it should be assumed that V, V R, R and there is no R, nor R Atrigger signal of a square or sawtooth waveform and having a frequency fis applied to the input terminal I, of a square wave frequency dividercircuit 0, and an output square wave V having a frequency f/2 isobtained from the output terminal 0,, of the circuit 0. This outputsquare wave V is then applied to the base of a transistor Tr2 through amixing resistor R Similarly, a sawtooth wave having a frequency f isapplied, through an input terminal 1,, to the base of a transistor Trlof a sawtooth buffer amplifier P, and the sawtooth output V, obtained atthe output terminal 0 at the emitter side of the transistor Trl (theoutput signal V is adjusted precisely to be equal in peak amplitude tothe square wave V is applied through another mixing resistor R (R R,,)to the base of the transistor Tr2. In this manner, the two signals V andV, at an equal peak amplitude are mixed together, and a sawtooth wave Vof a frequency f/2 is obtained at the emitter side of the transistor Tr2(operating as an emitter follower).

When the frequency of the sawtooth wave signal is to be further steppeddown, for instance to A, Vs, l/l6 the required number of the frequencydivider circuits as described must be connected in cascade, and eitherthe square-wave output signal from the terminal 0,, or the sawtoothoutput signal from the terminal 0 is applied to the input terminal ofthe square-wave frequency divider circuit included in the subsequentsawtooth wave frequency divider circuit, so that the frequency of thesawtooth wave is further stepped down.

However, when the conventional frequency divider circuit for a sawtoothwave is employed in chain (in cascade) for stepping down the frequency,some difficulties have been experienced, thus causing the connection ofthe frequency divider circuits to be excessively complicated and theoperations thereof to be unstable. 1

The principal reason for such difficulties is that the voltage utilityfactors for the square wave frequency divider circuit 0 and the sawtoothwave rendering circuit P are different from each other. Because of thisdifference in the voltage utility factors, the output levels of theformer circuit and the latter circuit operating in a distorsion-freerange are also made different, and if the power source voltages E A andE, are selected to be equal, the output level of the latter circuit willbe lower than the output level of the former circuit.

More specifically, while the output level V A (in crest value) of thesquare wave frequency divider circuit 0 is nearly equal to the powersource voltage E, (that is, V E the output voltage V, from the sawtoothwave producing circuit P is V =07E (for instance, equal to 0.85,).Accordingly, when the mixing resistors R, and R, are selected to beequal, the power source voltages E and E must be made different if bothof the output signals are to be mixed at the same level (V V However,even when the power source voltages E and E, are made different asdescribed above, the output level V, of the mixing circuit is stillreduced lower than the output level V This is because the voltage gainof the mixing circuit including the transistor Tr2 is approximately 0.8to 0.9.

Furthermore, because of the voltage dividing ratio due to the mixingresistors and the input impedance (finite value) of the bufi'eramplifying circuit including the transistor Tr2 as shown in FIG. 1, andalso because of the value of the voltage drop V which is not negligible,the DC voltage at the output terminal 0 is lower than that of the outputterminal 0 When a plurality of frequency divider circuits for thesawtooth wave as described are connected in cascade for stepping downthe frequency, the output levels of the subsequent stages arecontinuously lowered, and the DC potentials thereof are also lowered,the latter result making it difficult to maintain the operating point inthe operation characteristics of the subsequent stage at an adequate DCpotential.

SUMMARY OF THE INVENTION Therefore, the primary object of the presentinvention is to provide an improved frequency dividing circuit forsawtooth waves whereby all of the above described drawbacks of theconventional circuits can be substantially eliminated.

Another object of the present invention is to provide an improvedfrequency divider circuit for sawtooth waves wherein the output level(peak amplitude) of a sawtooth wave having a frequency f/2 is made equalto the original level of a sawtooth wave having a frequency f. i

A further object of the present invention is to provide an improvedfrequency divider circuit for sawtooth waves wherein the DC potential atthe output terminal of the sawtooth wave of a frequencyf/Z is made equalto the DC potential at the output terminal of the sawtooth producingcircuit having a frequency f.

Yet another object of the present invention is to provide an improvedfrequency divider circuit for sawtooth waves which can be connected incascade without reducing the output level of the signal, the frequencyof which is divided as required.

Still another object of the present invention is to provide an improvedfrequency divider circuit for sawtooth waves wherein only a single powersource voltage is required.

These and other objects of the present invention can be achieved by animproved frequency divider circuit for sawtooth wave which comprises acircuit for generating a sawtooth wave having a frequency f, a circuitfor generating a square wave having a frequency of a greater amplitude,mixing resistors through which the output signals from the abovementioned two circuits are mixed together, the mixing resistors being soselected that the ratio thereof is equal to the ratio of the sawtoothwave signal level and the square wave signal level from the respectivecircuits, and a buffer circuit for obtaining a desired output sawtoothwave of a frequency f/2- Preferably, the buffer circuit is furtherprovided with a biasing means for the base electrode so that the DCpotential of the base electrode is raised from that of the outputterminal of the sawtooth wave producing circuit by an amount equal tothe aforementioned voltage drop V across the base and emitter of thetransistor included in the buffer circuit, and, by so doing, the DCpotential of the output terminal of the buffer circuit is made equal tothat of the output terminal of the sawtooth wave producing circuit.

Preferably, the sawtooth wave producing circuit is arranged in the formof another buffer amplifier, and the square wave producing circuit isarranged in the form of a flip-flop.

And preferably, a single power source supplies power to all of the abovementioned circuits.

The invention will be better understood from the following detaileddescription when read in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is a block diagram showing a frequency divider circuit for asawtooth wave which constitutes a preferred embodiment of the presentinvention:

FIGS. 2(a) and 2(b) are a schematic diagram and a waveform chart to bereferred to for an explanation of the fundamental principle of thepresent invention, and

FIG. 3 is a graphical representation of the ratio V,x/V, which is variedin accordance with a coefficient k.

DETAILED DESCRIPTION OF THE INVENTION Referring first to FIG. 2 showingthe principle of how the frequency of a sawtooth wave is divided intoone half by mixing a square wave and a sawtooth wave, which it utilizedin the present invention, it is seen that a square wave V (in crestvalue) of a frequency f/2 and a sawtooth wave V, (also in crest value,and V, kV,,, where k is a coefficient) of a frequency f are mixedtogether in a specific phase-relation as indicated therein throughmixing resistors R and R,. R, is selected to be equal to KR, so that themixing voltage losses in these resistors are thereby made so difi'erentthat the mixing ratio of the square wave to the sawtooth wave will be k:l and as a result, the mixed components of the two waves become equalafter being mixed, thereby forming a sawtooth wave V,,x of a frequencyf/2.

In this case, the output level (in crest value) V can be empiricallyexpressed as More specifically, the level of the mixed wave V isgenerally different from the level of the input V,, the differencedepending on the value of k, and'when k 1, the output V becomes largerthan V,, whereby a kind of gain is indicated, which is the mostsignificant feature of this invention and is to be remembered. The valueof V, V, with variation of the coefficient k is shown in FIG. 3.

A preferred embodiment of this invention will now be described withreference to FIG. 1.

An output V,, of a frequency f/2 from a square wave frequency dividercircuit 0, which, in this example, is an ordinary flip-flop, is appliedto the base of a transistor Tr2 through a mixing resistor R,,.Simultaneously, another output V, having a frequency f and obtained froma sawtooth wave producing circuit P, which is in itself a bufiercircuit, is applied through another mixing resistor R, to the base ofthe transistor Tr2. To this base of the transistor Tr2, there isconnected a resistor R, for serving as a DC bias, and, when necessary,also a grounded resistor R The resultant output wave is obtained at theemitter of the transistor Tr2. Now the output V, (in crest value) islower than the output V, of the square wave (also in crest value), sothat V, =k V,,, wherein k 1.

While the values of the mixing resistors R A and R, as described arealso selected to satisfy a relation R, k R,,, both the square wave andthe sawtooth wave are mixed together under the same levels at thejunction X between the mixing resistors R and R,. For the convenience infurther explanation, it is assumed that the load impedance at thejunction point X is infinitive and also that the level (crest value) ofthe sawtooth wave at this point is V Then the above described relation V(2/1 +k) V, is satisfied, and it is also apparent from this equationthat V V.

However, the actual load impedance as considered from the point X, whichconsists of the input impedance of the transistor Tr2 and impedances ofother parallelly connected circuits, (in this case, R and R is notinfinitive, and hence the voltage at the point X is not exactly equal tothe above described V but is a velue V' slightly lower than the V Theoutput voltage V, obtained from the output terminal 0 is still lowerthan the voltage V because of the existence of the voltage drop V of thetransistor Tr2 and the load (not shown) connected to the output terminal0 Accordingly, by suitably'selecting the value of k, representing theratio between the resistor R, and R the advantageous result of theoutput level V, from the terminal 0 being equal to the output level V,of the sawtooth wave producing circuit can be obtained. For instance,when the above described voltage loss Vi /V is 0.8, the voltage ratio ofV21/V1 1.25 can be obtained by causing the value of k to be k 0.6, andthe advantageous result of V, V, can be realized.

As is apparent from the above description, according to the presentinvention, the resistance values of the mixing resistors R and R, (R, kR,,) are suitably selected so that the mixing ratio of the two signalsis not unity, that is, the value of k is a suitable value lower than 1,whereby the output levels V, and V (in Crest value) may be adjusted sothat V, V, or even Vg V1.

Furthermore, for the purpose of equalizing the DC potential at theoutput terminal 0, with the DC potential at the terminal 0,, forinstance, a bias adjusting resistor R, with or without another resistorR, may be employed as indicated in FIG. 1, in

which case the values of the resistors R and R are selected so that theDC potential at the junction point X is higher than that of the outputterminal 0 by a value equal to the above mentioned forward voltage dropV between the base and emitter of the transistor Tr2. By so doing,several of the frequency divider circuits as described above may also beconnected sequentially with the operating point in each stage beingmaintained constant.

In addition, the output level V,, for the square wave signal may beselected larger than the output level V for the sawtooth wave signal,and for this reason, a single power source voltage may be commonlyemployed for all of the component circuits such as the above describedsquare wave producing circuit, of a good power voltage utility factor,sawtooth wave producing circuit of a little worse utility factor and themixing buffer circuit. Thus, the organization of the frequency dividercircuit for sawtooth wave can be greatly simplified, and the voltageutility factors in respective stages of the cascade connected circuitscan be much improved.

Although the present invention has been described with respect to apreferred embodiment thereof, it will be apparent to those skilled inthe art that various modifications and alterations thereof may also bepracticed without departing from the true spirit and scope of thepresent invention. For instance, the square wave producing circuit maybe any one of conventional circuits other than the above describedflip-flop, and the transistors in the buffer circuits may bereplaced byfield-effect transistors.

I claim:

1. A frequency dividing and mixing circuit comprising: a first circuithaving an output terminal and producing a sawtooth wave with a firstpeak amplitude and a first frequency; a second circuit having an outputterminal and producing a square wave with a second peak amplitudegreater than said first peak amplitude and a frequency which is one-halfof said first frequency; a bufier circuit connected to said first andsecond circuits and producing a resultant sawtooth wave of frequencywhich is one-half of said first frequency and with a peak amplitudegreater than said first peak amplitude; a first mixing resistorconnected between the output terminal of said first circuit and an inputterminal of the buffer circuit; and a second mixing resistor connectedbetween the output tenninal of said second circuit and the inputterminal of the buffer circuit, said first and second resistances beingof such resistance values that the ratio of the first resistance to thesecond resistance is equal to the ratio of said f'ust peak amplitude tosaid second peak amplitude.

2. A frequency dividing and mixing circuit as defined in claim 1 whereina biasing means is included in said bufier circuit so that a DCpotential at an output of the buffer circuit is made equal to the DCpotential at the output of said first sawtooth wave producing circuit,whereby a required number of sawtooth wave frequency dividers can beconnected in cascade.

3. A frequency dividing and mixing circuit as defined in claim 1 whereinsaid sawtooth wave producing first circuit, said square wave producingsecond circuit, and said bufi'er circuit 'are all provided withconnecting means to connect them to a common power source.

4. A frequency dividing and mixing circuit as defined in claim 1 whereinsaid second circuit producing a square wave comprises a flip-flopcircuit.

5. A frequency dividing and mixing circuit as defined in claim 1 whereinsaid buffer circuit is in the form of an emitter follower amplifier.

1. A frequency dividing and mixing circuit comprising: a first circuithaving an output terminal and producing a sawtooth wave with a firstpeak amplitude and a first frequency; a second circuit having an outputterminal and producing a square wave with a second peak amplitudegreater than said first peak amplitude and a frequency which is one-halfof said first frequency; a buffer circuit connected to said first andsecond circuits and producing a resultant sawtooth wave of frequencywhich is one-half of said first frequency and with a peak amplitudegreater than said first peak amplitude; a first mixing resistorconnected between the output terminal of said first circuit and an inputterminal of the buffer circuit; and a second mixing resistor connectedbetween the output terminal of said second circuit and the inputterminal of the buffer circuit, said first and second resistances beingof such resistance values that the ratio of the first resistance to thesecond resistance is equal to the ratio of said first peak amplitude tosaid second peak amplitude.
 2. A frequency dividing and mixing circuitas defined in claim 1 wherein a biasing means is included in said buffercircuit so that a DC potential at an output of the buffer circuit ismade equal to the DC potential at the output of said first sawtooth waveproducing circuit, whereby a required number of sawtooth wave frequencydividers can be connected in cascade.
 3. A frequency dividing and mixingcircuit as defined in claim 1 wherein said sawtooth wave producing firstcircuit, said square wave producing second circuit, and said buffercircuit are all provided with connecting means to connect them to acommon power source.
 4. A frequency dividing and mixing circuit asdefined in claim 1 wherein said second circuit producing a square wavecomprises a flip-flop circuit.
 5. A frequency dividing and mixingcircuit as defined in claim 1 wherein said buffer circuit is in the formof an emitter follower amplifier.